What Causes Momentary Paralysis In The Morning?

When I woke up this morning I was completely paralysed. This only lasted a few moments, but I was unable to even open my eyes, and i could hear my name being whispered. I assure you it was not a dream: I was fully concious and desperate to move get up. I am now terrified that it was paranormal activity, please tell me if there is a medical explanation. (I am under huge stress (exams) at the moment if that is relevant)